As computer terminals become more and more complex and perform a wider variety of tasks, it becomes necessary for a terminal operator to remember each key's special function. In some instances, such as an editor program on a data entry terminal, a single key may perform a variety of functions, depending upon the mode of the terminal or program. Depending upon how many keys are programmed for special or multiple functions, it may be confusing and difficult to keep track of the function of each key.
The function of eacy key may be identified by having a keyboard with many dedicated function keys. Another solution to keep track of the function of a key is to have a chart displayed near the keyboard describing the function of each key. Removable key cap covers, or labels may be attached to each key to identify its function. An alternative to the above is to have the operator remember the function of each programmed key. Obviously there are disadvantges to each of the above methods for identifying the function of a programmed key. When a key is dedicated, its function cannot be changed. Changing key caps or labels is time consuming and the caps and labels can be lost. Unless only one operator uses the terminal, remembering what key has been programmed to which function is not practical.
Key identification has been done using various types of displays, including those built into the key. In practice, once the display has been incorporated into the key, it is not easily modified or reprogrammed to indicate a change of function of the key. Display keys are described in U.S. Pat. Nos. 3,758,785, 3,787,837, and 3,856,605. However, none of these patents describes a programmable function key in which the key displays an indication of the programmed function.